def test_removals(self):
        c = SetUpdateClause('s', {1, 2}, previous={1, 2, 3})
        c._analyze()
        c.set_context_id(0)

        self.assertIsNone(c._assignments)
        self.assertIsNone(c._additions)
        self.assertEqual(c._removals, {3})

        self.assertEqual(c.get_context_size(), 1)
        self.assertEqual(str(c), '"s" = "s" - %(0)s')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {'0': {3}})
    def test_no_update(self):
        """ tests an unchanged value creates an empty update statement """
        c = SetUpdateClause('s', {1, 2}, previous={1, 2})
        c._analyze()
        c.set_context_id(0)

        self.assertIsNone(c._assignments)
        self.assertIsNone(c._additions)
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 0)
        self.assertEqual(str(c), '')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {})
    def test_update_empty_set(self):
        """tests assigning a set to an empty set creates a nonempty
        update statement and nonzero context size."""
        c = SetUpdateClause(field='s', value=set())
        c._analyze()
        c.set_context_id(0)

        self.assertEqual(c._assignments, set())
        self.assertIsNone(c._additions)
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 1)
        self.assertEqual(str(c), '"s" = %(0)s')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {'0': set()})
    def test_additions_and_removals(self):
        c = SetUpdateClause('s', {2, 3}, {1, 2})
        c._analyze()
        c.set_context_id(0)

        self.assertIsNone(c._assignments)
        self.assertEqual(c._additions, {3})
        self.assertEqual(c._removals, {1})

        self.assertEqual(c.get_context_size(), 2)
        self.assertEqual(str(c), '"s" = "s" + :0, "s" = "s" - :1')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {'0': {3}, '1': {1}})
    def test_additions(self):
        c = SetUpdateClause('s', set([1, 2, 3]), previous=set([1, 2]))
        c._analyze()
        c.set_context_id(0)

        self.assertIsNone(c._assignments)
        self.assertEqual(c._additions, set([3]))
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 1)
        self.assertEqual(str(c), '"s" = "s" + %(0)s')

        ctx = dict()
        c.update_context(ctx)
        self.assertEqual(ctx, {'0': set([3])})
    def test_update_from_none(self):
        c = SetUpdateClause('s', {1, 2}, None)
        c._analyze()
        c.set_context_id(0)

        self.assertEqual(c._assignments, {1, 2})
        self.assertIsNone(c._additions)
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 1)
        self.assertEqual(str(c), '"s" = :0')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {'0': {1, 2}})
    def test_additions(self):
        c = SetUpdateClause('s', {1, 2, 3}, previous={1, 2})
        c._analyze()
        c.set_context_id(0)

        self.assertIsNone(c._assignments)
        self.assertEqual(c._additions, {3})
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 1)
        self.assertEqual(str(c), '"s" = "s" + %(0)s')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {'0': {3}})
    def test_no_update(self):
        """ tests an unchanged value creates an empty update statement """
        c = SetUpdateClause('s', set([1, 2]), previous=set([1, 2]))
        c._analyze()
        c.set_context_id(0)

        self.assertIsNone(c._assignments)
        self.assertIsNone(c._additions)
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 0)
        self.assertEqual(str(c), '')

        ctx = dict()
        c.update_context(ctx)
        self.assertEqual(ctx, dict())
    def test_null_update(self):
        """ tests setting a set to None creates an empty update statement """
        c = SetUpdateClause('s', None, {1, 2})
        c._analyze()
        c.set_context_id(0)

        self.assertIsNone(c._assignments)
        self.assertIsNone(c._additions)
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 0)
        self.assertEqual(str(c), '')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {})
    def test_update_empty_set(self):
        """tests assigning a set to an empty set creates a nonempty
        update statement and nonzero context size."""
        c = SetUpdateClause(field='s', value=set())
        c._analyze()
        c.set_context_id(0)

        self.assertEqual(c._assignments, set())
        self.assertIsNone(c._additions)
        self.assertIsNone(c._removals)

        self.assertEqual(c.get_context_size(), 1)
        self.assertEqual(str(c), '"s" = %(0)s')

        ctx = {}
        c.update_context(ctx)
        self.assertEqual(ctx, {'0' : set()})